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JEE Main 2026 · 6 Apr · Shift 1, Physics question 47

An unpolarized light of intensity IoI_o passes through polarizer and then through a certain optically active solution and finally it goes to analyser. If the angle between analyser and polariser is 0° and intensity of light emerged from analyser is 38Io\dfrac38I_o, the angle of rotation of the light by the solution with respect to analyser is ________ degrees.

Answer and worked solution

Official answer: 30

After the polariser: Io2\tfrac{I_o}2.

Through the analyser (parallel to the polariser). If the solution rotates the plane by θ:
Io2cos⁡2θ=38Io ⇒ cos⁡2θ=34 ⇒ θ=30∘.\frac{I_o}2\cos^2\theta=\frac38I_o\ \Rightarrow\ \cos^2\theta=\frac34\ \Rightarrow\ \theta=30^\circ.

Answer: 30

Topics:Polarisation and Brewster's law
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